US3757967A

US3757967A - Storage rack with dual safety bridge

Info

Publication number: US3757967A
Application number: US00187609A
Authority: US
Inventors: T Colbridge
Original assignee: Rack Engineering Co
Current assignee: Rack Engineering Co
Priority date: 1971-10-08
Filing date: 1971-10-08
Publication date: 1973-09-11
Anticipated expiration: 1990-09-11

Abstract

A storage rack installation has two rows of multi-shelf racks with an intervening aisle and at least some of the shelves have track rails extending from front to back on which the wheels of a load-carrying dolly ride. Spring-projected latch pins at the front of each such shelf normally restrain its dolly against forward travel on the shelf. Dual bridge bars are removably rested at one end on a selected shelf at one side of the aisle and at the other end on a shelf across the aisle, each of which has a rail thereon to register with a rail on the selected shelf. Each bar has hooks that straddle the track rail of the selected shelf to align the shelf rail and rail of the bridge bar and each has an extension that depresses the nearby latch pin so that when both bridge bars are in place both latch pins are depressed and the dolly can roll at least part way off the selected shelf onto the bridge bars. A slide bolt on each bridge bar engages the selected shelf to selectively hold the bridge bar against vertical movement.

Description

iJted States Patent 1 1 1 3,757,967 olbridge 1 Sept. 11, 1973 STORAGE RACK WITH DUAL SAFETY Primary ExaminerGerald M. Forlenza BRIDGE Assistant Examiner-D. W. Keen 75 lnventor: Thomas D. Colbridge, Chalk Hill, Pa. Parmelee [73] Assignee: Rack Engineering Company,

Connellsville, Pa. ABSTRACT [22] Filed: Oct. 8, 1971 A storage rack installation has two rows of multi-shelf racks with an intervenin aisle and at least some of the [21 1 Appl' 181609 shelves have track rails eitending from front to back on I which the wheels of a load-carrying dolly ride. Spring- [52] [1.8. Ci. 2l4/16.4 R, 14/42, 238/225, projected latch pins at the front of each such shelf nor- 238/227 mally restrain its dolly against forward travel on the [51] Int. Cl E01b 11/58 shelf. Dual bridge bars are removably rested at one end [58] Field of Search 214/l6.4 A, 38 D, on a selected shelf at one side of the aisle and at the 2l4/l6.l EB, 16.4 R; 104/127, 128, 129, 3]; other end on a shelf across the aisle, each of which has 211/162, 176, 177; 14/41, 42, 71, 72; a rail thereon to register with a rail on the selected 238/225, 227 shelf. Each bar has books that straddle the track rail of the selected shelf to align the shelf rail and rail of the [56]. References Cited bridge bar and each has an extension that depresses the UNITED S ES TENTS nearby latch pin so that when both bridge bars are in 268 74s 12/1882 Stewart 214/164 A Place latch Pins are depressed and the dolly can 548:090 0/1895 Puffer I 214/16 4-A roll at least part way off the selected shelf onto the 2,053,969 9/1936 Olds I I I 2 4 3 D bridge bars. A slide bolt on each bridge bar engages the 3,561,365 2/1971 Rooklyn 104/127 selected shelf to selectively hold the bridge bar against 2,726,774 12/1955 Newsom 214/16.1 EB vertical movement. 3,337,069 8/1967 Burger 2l4/l6.4'R

11 Claims, 6 Drawing Figures Patented Sept. 11, 1973 2 Sheets-Sheet 1 Patented Sept. 11, 1973 2 Sheets-Sheet 2 1 STORAGE RACK WITH DUAL SAFETY BRIDGE This invention relates to multi-shelf storage racks wherein there is a wheeled dolly on each of some or all of the shelves and to a safety bridge structure to enable a dolly at a selected shelf to be wheeled from the shelf to an exposed position at the front of the shelf where a crane or hoist may place a load on the dolly or remove a load therefrom.

In U.S. Pat. No. 2,729,342 granted Jan. 3, 1956 there is disclosed a type of multi-shelf rack where there are several equally spaced pairs of one front and one back upright columns which are vertically notched and shelves extending between each two pairs of uprights have mounting means at their corners engaged in the notches of the uprights so that the shelves may be arranged at different elevations between the uprights on which they are supported. Originally, storage racks of this type were commonly used where the object or load to be stored was placed on a pallet and raised into place by a fork-lift that could place the loaded pallet on a shelf or remove the loaded pallet from a shelf. How ever, in many instances the racks'have been built to a height where they could not be loaded or unloaded in this way and increasingly heavy loads have been placed on the shelves, as for example spare parts of heavy machinery weighing perhaps a ton or two tons or more. These developments and the fact that the racks are often arranged in confronting rows with insufficient room in the aisles between the rows to enable a fork-lift truck to be maneuvered has led to the use of an'overhead traveling crane or hoist for bringing a load to the rack or to carry it away. A difficulty, however, arises from the fact that the crane must lift or lower the load vertically, and with one shelf below another considerable labor is required to get a load hanging from the hoist or crane onto a shelf or removing it from ashelf. Not only are such operations time consuming and laborious, but they may be hazardous.

To facilitate the loading or unloading of the shelves, a pair of rails have been mounted onthe shelves extending from front to backand a wheeled dolly is carried on these rails to support the load to be stored. A pair of removable bridge bars have been employed, one end of each of which is hooked onto the shelf and the other end supported on a shelf across the aisle. Each bridge bar has a rail that registers with one of therails on the shelf, so that a dolly'could be rolled from a shelf onto the bridge bars sufficiently to give the dolly the required exposure to the crane or hoist for depositing a load on the dolly or removing a load therefrom.

Such arrangements, however, may result in spills or near spills'caused by some misalignment or accidental movement of a bridge bar, or for the reason that a dolly might roll 011' a shelf entirely by accident or carelessness when thereare no bridge bars in place at all.

According to the present invention there is a latch pin, and preferably two latch pins on the front of each shelf which is spring-projected into the path of travel of a dolly to normally prevent the dolly from moving on the shelf rails in a direction to leave the shelf. Each latch pin is so positioned that a bridge bar must be exactly positioned at the front of the shelf rail to release the latch pin. With two latch pins so positioned, two bridge bars must be exactly in the right alignment with the shelf rails to release both latches to enable the dolly to roll from the shelf onto the bridge bars. Also each bridge bar has a bolt operable to clamp the bar in position on the shelf, and thereby restrain it against accidental movement.

In the accompanying drawing showing a preferred embodiment of the invention:

FIG. 1 is a side elevation of two confronting racks with the intervening aisle and the dual bridge bars in place, the dolly being shown in phantom outline on the bridge bars and in full lines on another shelf;

FIG. 2 is a top plan view of a typical rack and shelf with the dolly removed and with the uprights shown in section and positions of adjoining shelves are also shown;

FIG. 3 is a transverse fragmentary vertical section through the shelf of FIG. 1 showing a latch in elevation and the dolly being restrained by the latch, the section being on line IIIIII of FIG. 1 but on a larger scale;

FIG. 4 is a view similar to FIG. 3 ant showing one of the bridge bars clamped in position on the shelf and the latch pin depressed;

FIG. 5 is a transverse vertical section in the plane of line V-V of FIG. 4; and

FIG. 6 is a side elevation of one of the bridge bars.

Referring to the drawings, the adjustable shelf racks have notched front uprights 5 and rear uprights 6. There are shelves, designated generally as 7 at various levels. Each shelf has a mounting element 8 on each corner engaged in the notches of a pair of

uprights

5 and 6 at each end. Each shelf, which is comprised ofstructural sections, has a front beam 9 of channel section with the web of the channel vertical and the flanges facing outwardly or forwardly and its length together with the mounting elements 8 at each end spans the distance between two uprights with the mounting elements engaged in the notched edges of the uprights. There is a similar beam 10. at the rear of the shelf. There is atransverse section or cross member 11 near each end of the shelf and there may be other transverse members or struts 12 intermediate the ends. The shelves of this invention each have a rail 13 thereon over the top of each cross member 11 in the form of an inverted angle bar forming an inverted V-section. The front end of each rail extends across the top of the front beam 9 but at the rear end of each rail there is a vertical stop member 14 on the top of the section 10 to limit the travel of the dolly hereinafter described and prevent it from rolling off the back of the shelf.

The'dolly itself is designated 20 and has a structural bed-frame or chassis with a channel section 21 across the front and a similar section 22 across the back. There are front and rear connecting members and near each end of the dolly are front and rear grooved wheels 23 positioned to travel on the shelf rails 13 with grooves in the wheels conforming to the inverted V- shape of the rails. The dolly usually has a deck plate and may have a surrounding guard rail above the level of the deck to retain a load in position on the dolly.

All of the structure so far described is generally known in the art, and the racks as indicated in FIG. 1 are commonly arranged in confronting parallel rows, such as A and B in FIG. 1 with an intervening aisle C therebetween.

According to the present invention there are one or more, preferably two safety latches on the shelf to prevent a dolly from perhaps spontaneously rolling off a shelf or being accidentally removed therefrom. Two of these units have been indicated on the shelf of FIG. 2 and are similarly located and positioned on all of the shelves of the racks which are designed to have a dolly thereon, and they are designated generally as 25. Each unit comprises a casing or barrel 26 welded to the rear face of the front beam member 9 of the shelf. It has a pin 27 that is resiliently projected upwardly by a spring 28 confined between the pin and a closure at the lower end of the barrel. The pin has a depending stem 29 that is slidably passed through the closure at the lower end of the barrel and a stop element, such as a disk 30, fixed on the end of the stem limits the upward travel of the When the pin is projected to the uppermost limit of its movement as shown in FIG. 3, it is in the path of travel of the skirt or front section 21 of the dolly so that the dolly is normally confined against movement on the rails 13 by the stop members 14 at the rear of the shelf and the latch pin or pins 27 at the front. To roll the dolly forward, the latch pin or pins must be depressed.

As above stated, it is desirable to have two of these latch units 25 on the front beam of the shelf. The units are placed on the beam 9 close to but clear of the rails 13. Preferably one is at each inside corner formed where the cross members 11 intersect with and are welded to the front section 9. In this position they are inside the front section 9 and close to the rails. 13.

When it is necessary to have access to the dolly, either for loading or unloading it, two bridge bars 35 are put in place in line with the rails 13 on the shelf, one end of the bridge bar being supported on the beam 9 of the selected shelf and the opposite ends of these bars are rested on the beam 9 of the confronting shelf across the aisle. For purposes of illustration it may be assumed that the selected shelf is in the stack A at the right and the supporting shelf for the remote ends of the bridge bars is in stack B.

Each bridge bar comprises a straight structural main section 36, preferably an I-beam as shown in FIG. with a vertical web and top and bottom flanges. It is cut off square at each end, and the distance between its ends is slightly less than the minimum width of the aisle at shelf level. For ease of handling it is desirable to make it of aluminum or aluminum alloy. Along the top of the bar there is an inverted V-shape rail 37 the same as the rail 13 on the shelf. It extends from that end of the bar which will receive the dolly, in the assumed example, the right end, part way along the full length of the bar to a stop 37a at the left end of the rail 37.

At said end, that is the right end as shown in FIG. 1, there is a side plate 38 welded, or otherwise immovably affixed to the main section at one side thereof and a second side plate 39 on the other. As seen in FIG. 5 both plates are of the same height with their top edges above the peak of the rail 37. Each of these two side plates projects beyond the end of the rail 36 and theprojecting end is cut away to provide an opening 40 (see FIG. 4) with a flat upper edge 41 and a projecting extension 42 having a depending lip or nib 43 at its outer edge, providing a hook structure that will set down over the beam 9 of the shelf, as shown in FIG. 4, that will support the bridge bar on the shelf and hold it against endwise movement..The hook portions so formed on

plates

38 and 39 are so located that when the bridge bar is supported on the beam structure 9 of the shelf the top of the rail 37 is exactly level with the top of a matching rail 13 on the shelf with only a slight space between the confronting rail ends. The distance between the plate extensions 42, as well as the plates themselves that the hook-forming extensions will straddle the ends of the rail 13 where it extends across the section 9 to align the rail 37 on the bridge bar with the rail 13 of the shelf, and restrain the bridge bar against any sidewise shifting or displacement after the bridge bar has been put into position on the shelf.

One of the plates 38 of the bridge bar, which may be termed the inside plate because it faces toward the other one, has a short length of angle bar 44 welded to the outside thereof with the end of this bar extending beyond the plate extension 42 (see FIGS. 4 and 5) and with its vertical leg against the plate 38 and its other leg horizontal. This angle is so positioned that when the bridge bar is hooked into place, as above described, the horizontal leg 44 of the angle section will bear down on the top of the latch pin 27 and depress the latch pin below the skirt or structural section 21 at the front of the dolly. With two latch pins, both will be depressed only when both bridge bars are in place, and of course, when this happens the dolly may roll forward onto the bridge bars to the point where the stops 37a prevent further outward travel of the dolly.

At theother end of the main bar section 36, that is the left end as here shown, there are also welded or otherwise fixed two metal plates 46 (see FIG. 6) one at each side of the bar and they too have their upper edges extending well above the top of the bar. They have integral extensions 47 that project beyond the end of the bar 35 at a level to be rested on the beam 9 of the shelf across the aisle with the bar substantially level when the bar is so supported on the two opposed shelves. The length of the supporting extensions 47 is adequate to accommodate for a wide variation of the width of the aisle at various positions in the two racks because with racks such as these, considerable tolerances must be provided.

Finally, on one of the

side plates

38 or 39, preferably the inside ones, there is a sliding bolt to hold the bridge bar against accidental removal after it has been put in place. To this end there are two aligned spaced guides 50 and 51 at the lower end of the side plate 35 and welded thereto. There isa bolt 52 slidably extending through both guides and the forward end of the bolt is tapered at 53. There is a U-shaped handle 5 having one leg attached to the bolt between the two guides and its other end attached to the rear end of the bolt. When the bridge bar is put into place, a workman forces the bolt forward, or as here shown to the right, wedging the forward end of the bolt under the lower flange of the shelf-beam section 9 to the position shown in FIG. 4. To remove a bridge bar, the bolt must first be retracted until its tapered end will clear the shelf section 9. The handle limits the travel of the bolt, and as here shown the bolt may be rotated about its axis for purposes of convenience.

With the arrangement herein described, a dolly may not be rolled forward from the shelf until the latch pin or pins are depressed and these will only be depressed when the bridge bars are placed in position. When the bridge bars are in position the rails 37 of the bridge bars align vertically and horizontally with the rails 13 on the shelf and the parallel side plates prevent lateral motion of the bar with respect to the shelf rail. In fact, when the extensions 42 of the

plates

38 and 39 are lowered over the rail ends 13 they guide the bridge bar into proper alignment. Similarly the extensions 47 of the g plates 46 at the opposite ends of the bar will fit over the rails 13 of the confronting shelf to keep the bridge bars parallel. After each bridge bar is put into place, its bolt 52 will be forced into bar-holding position, whereby maximum protection is provided against accidental displacement of the bars and the bolts then resist the upward pressure of the latch pins. The latch pins are only retracted from the position where they prevent travel of the dolly when both the bridge bars are in place. Careless misalignment cannot result in the improper release of the dolly.

The stops 37a on the ends of the rails 37 are usually located in such position that when the dolly is rolled onto the bridge bars for loading or unloading, the rear wheels of the dolly will always remain on the shelf rails 11 and thereby keep the load more nearly in the vertical plane of the columns while adequately exposing the deck of the dolly for loading or unloading by a crane or hoist. The latching pins are biased into latching position by strong springs so as to resist accidental release thereof, and the locking bolt 52 when in locking position counteracts the upward pressure of the latch pin against the lifting bar as well as otherwise insuring against accidental displacement of a bridge bar.

- lclaim:

1. Storage apparatus comprising in combination:

a. two confronting rows of multi-shelf storage racks with an intervening aisle, the shelves being supported by spaced vertical columns at each end, the shelves being formed of structural sections including a beam across the front of each shelf, each shelf 1 having two parallel rails extending thereacross from front to back, the front ends of the rails extending across the beam at the front of the shelf,

b. a dolly on at least some ,of the shelves having wheels that roll on and are guided by the rails,

c. a latch unit on said beam comprising a pin that is resiliently urged upwardly into an extended position where it obstructs the movement of the dolly off the front of the shelf but which may be depressed to a position out of dolly-obstructing position, dual bridge bars with rails thereon, each bar having an end portion that removably hooks over said beam on the shelf at each side of one of the rails on the shelf to support said end of the bridge bar on the beam with its rail aligned with the rail on the shelf, and

. means on at least one of the two bars for depressing the pin of said latch and holding it depressed only when said end of the bridge bar is positioned on the shelf beam where its rail is aligned with the rail on the shelf. 1

2. Storage apparatus as defined in claim 1 wherein there are two latch units on the shelf beam, one adjacent each rail on the shelf and each of the dual bridge bars has means for depressing that latch pin most closely adjacent that shelf rail with which the railon the bridge bar is aligned and holding it depressed only while the said end of the bar is in rail-aligning position on the shelf beam whereby the dolly cannot be rolled off the shelf until both bridge bars are in position to receive it.

3. Storage apparatus as defined in claim 1 wherein said end portion of each bar which hooks over the beam on the shelf straddles a shelf rail in such manner as to hold the bar against movement sideways along the shelf beam.

4. Storage apparatus as defined in claim 3 wherein there is a manually operable bolt on the same end of each bridge bar arranged to be projected under the shelf beam over which the said end of the bridge bar is hooked to releaseably lock the bridge bar against vertical movement after it is in the position where the rail on the bar is aligned with a rail on the shelf.

5. For use in a storage apparatus where there are confronting multi-shelf storage racks with an aisle therebetween and at least some of the shelves of the rack have a structural beam across the front thereof and each shelf also has two spaced track rails extending from across the beam at the, front of the shelf to the rear of the shelf and a dolly on the shelf which rests on and is movable along said rails, the invention compris-ing a pair of bridge bars for use therewith, each bridge bar being:

a. of an overall length sufficient to be supported at one end on the shelf beam of a first rack at one side of the aisle and be supported at the other end of the confronting rack across the aisle,

h. each bar comprising a main bar section, said section having: 7

' l. a track rail along'the top thereof of the same section as the track rail on the shelf,

2. means at one end arranged to hook over the shelf beam of a shelf on said first rack, I

3. said last-named means interlocking with means on the shelf for restraining the bar againstlateral movement on the shelf beam only'when the track rail on the beam is in alignment with a trackrail on the shelf, and comprising twometal plates, one secured to each side of the main bar section and extending forwardly from the main bar section, the forward extension of each plate forming a hook portion shaped to rest on the top of the shelf beam and engage the back surface of said shelf beam, said hook portions being'at an elevation where the track rail on the main bar section will meet and align with one of the track rails on the bridge, said hooklike extensions being posi tioned on the main bar so-that they straddle a track rail on the shelf. when the respective track rails are aligned and thereby restrain the bar against lateral movement'on the shelf beam.

6. The invention defined in claim 5 wherein there are two plates secured to the other end of the main bar section, one at each side of said section arranged to rest on a correspondingly positioned shelf of the opposite rack and straddle a track rail of said correspondingly positioned shelf to thereby aid in keeping the pair of bars when in place parallel.

7. The invention defined in claim 5 wherein there is a means on said one end of thebar arranged to engage the shelf beam when the respective track rails of the shelf and bar are aligned to releasably hold the bridge bar against vertical movement relative to said shelf beam.

8. The invention defined in claim 7 wherein said lastnamed means comprises a reciprocable bolt on one of said side plates movable axially into and out of a locking position against the underside of the shelf beam.

9. The invention defined in claim 5 wherein there is a means on said end of the bridge bar operable only when the bridge bar is hooked over said shelf beam with the rail of the bridge bar aligned with a rail on the shelf for holding in an inactive position latching means on the shelf which is effective to restrain a dolly on the shelf against movement on said track rails when not inactivated by the bridge bar.

10. The invention defined in claim 9 wherein the lastnamed means on the bridge bar presses down on the latch pin on the shelf beam that is spring-biased to push upwardly into the path of travel of the dolly, and there is a reciprocable bolt at said end of the bridge bar axially movable into and out of locking posi-tion with the shelf beam to oppose the lifting force of said springbiased latch pin against said end of the bridge bar.

11. A storage apparatus comprising in combination:

a. two confronting rows of racks with an intervening aisle and shelves at selected levels in the racks of each row, the shelves having track rails extending from front to back and having a dolly movable along said rails, the shelves having means at the back thereof to limit a pair of spring-biased depressable latch pins at the front that normally restrain the dolly from forward movement off the shelf,

b. a pair of bridge rails, each of which has:

1. a first end constructed to hook onto a selected shelf in one row and a second end to be supported on a shelf of the opposite row,

2. a track rail extending therealong from said first end toward said second end,

3. said first end having means that hold the bridge bar against sidewise or endwise movement on the shelf when the track rail on the bridge bar is aligned with a track rail on the shelf, and

4. means on said first end operable to depress one of said latch pins only when the bar is so positioned on the shelf with its track rail aligned with a track rail on the shelf,

c. whereby said pair of bridge bars may be positioned on any selected shelf of either row with the first ends thereof engaged with the selected shelf to depress the latch pins of the sleected shelf whereby only then may the dolly move from the track rails on the shelf to the track rails on the bridge bars.

1 w a a:

Claims

1. Storage apparatus comprising in combination: a. two confronting rows of multi-shelf storage racks with an intervening aisle, the shelves being supported by spaced vertical columns at each end, the shelves being formed of structural sections including a beam across the front of each shelf, each shelf having two parallel rails extending thereacross from front to back, the front ends of the rails extending across the beam at the front of the shelf, b. a dolly on at least some of the shelves having wheels that roll on and are guided by the rails, c. a latch unit on said beam comprising a pin that is resiliently urged upwardly into an extended position where it obstructs the movement of the dolly off the front of the shelf but which may be depressed to a position out of dollyobstructing position, d. dual bridge bars with rails thereon, each bar having an end portion that removably hooks over said beam on the shelf at each side of one of the rails on the shelf to support said end of the bridge bar on the beam with its rail aligned with the rail on the shelf, and e. means on at least one of the two bars for depressing the pin of said latch and holding it depressed only when said end of the bridge bar is positioned on the shelf beam where its rail is aligned with the rail on the shelf.

2. Storage apparatus as defined in claim 1 wherein there are two latch units on the shelf beam, one adjacent each rail on the shelf and each of the dual bridge bars has means for depressing that latch pin most closely adjacent that shelf rail with which the rail on the bridge bar is aligned and holding it depressed only while the said end of the bar is in rail-aligning position on the shelf beam whereby the dolly cannot be rolled off the shelf until both bridge bars are in position to receive it.

2. means at one end arranged to hook over the shelf beam of a shelf on said first rack,

3. said last-named means interlocking with means on the shelf for restraining the bar against lateral movement on the shelf beam only when the track rail on the beam is in alignment with a track rail on the shelf, and comprising two metal plates, one secured to each side of the main bar section and extending forwardly from the main bar section, the forward extension of each plate forming a hook portion shaped to rest on the top of the shelf beam and engage the back surface of said shelf beam, said hook portions being at an elevation where the track rail on the main bar section will meet and align with one of the track rails on the bridge, said hooklike extensions being positioned on the main bar so that they straddle a track rail on the shelf when the respective track rails are aligned and thereby restrain the bar against lateral movement on the shelf beam.

4. means on said first end operable to depress one of said latch pins only when the bar is so positioned on the shelf with its track rail aligned with a track rail on the shelf, c. whereby said pair of bridge bars may be positioned on any selected shelf of either row with the first ends thereof engaged with the selected shelf to depress the latch pins of the sleected shelf whereby only then may the dolly move from the track rails on the shelf to the track rails on the bridge bars.

5. For use in a storage apparatus where there are confronting multi-shelf storage racks with an aisle therebetween and at least some of the shelves of the rack have a structural beam across the front thereof and each shelf also has two spaced track rails extending from across the beam at the front of the sHelf to the rear of the shelf and a dolly on the shelf which rests on and is movable along said rails, the invention compris-ing a pair of bridge bars for use therewith, each bridge bar being: a. of an overall length sufficient to be supported at one end on the shelf beam of a first rack at one side of the aisle and be supported at the other end of the confronting rack across the aisle, b. each bar comprising a main bar section, said section having:

7. The invention defined in claim 5 wherein there is a means on said one end of the bar arranged to engage the shelf beam when the respective track rails of the shelf and bar are aligned to releasably hold the bridge bar against vertical movement relative to said shelf beam.

10. The invention defined in claim 9 wherein the last-named means on the bridge bar presses down on the latch pin on the shelf beam that is spring-biased to push upwardly into the path of travel of the dolly, and there is a reciprocable bolt at said end of the bridge bar axially movable into and out of locking posi-tion with the shelf beam to oppose the lifting force of said spring-biased latch pin against said end of the bridge bar.

11. A storage apparatus comprising in combination: a. two confronting rows of racks with an intervening aisle and shelves at selected levels in the racks of each row, the shelves having track rails extending from front to back and having a dolly movable along said rails, the shelves having means at the back thereof to limit a pair of spring-biased depressable latch pins at the front that normally restrain the dolly from forward movement off the shelf, b. a pair of bridge rails, each of which has: